The triplet PES (blue) has a shallow physisorption (physi.) well with O 2.3 A above the surface and exhibits chemisorption (chemi.) at the top and bridge sites with binding energies of 0.65 and 0.51 eV, respectively. The singlet PES (red) does not have a physisorption well but exhibits strong chemisorption at the bridge site (1.91 eV binding energy relative to the O(3P) asymptote). The two PESs cross at a seam of intersection located near the physisorption barrier on the triplet PES. Note that, due to intrinsic errors in the DFT calculations, the calculated gas-phase splitting between the O(1D) and O(3P) states is only 1.3 eV, whereas experimentally this quantity is known to be 1.97 eV. Therefore, the singlet PES was shifted upwards by 0.7 eV in the O(1D) scattering simulations to match the 1D/3P energy gap of the atomic oxygen. TS, transition state.
